Powder feeding assembly

ABSTRACT

A POWDER FEED ASSEMBLY HAVING A HOUSING PROVIDED WITH A POWDER RESERVOIR AND A POWDER FLUIDIZING CHAMBER. THE RESERVOIR HAS A SUMP AT ITS LOWER END AND A CONVEYOR IN THE SUMP TO DELIVER POWDER TO THE FLUIDIZING CHAMBER. A CONDUIT DELIVERS A CARRIER GAS UNDER PRESSURE TO THE CHAMBER. ANOTHER CONDUIT CONNECTS THE CHAMBER WITH THE RESERVOIR TO EQUALIZE THE PRESSURE THEREIN AND VALVE MEANS CAN VARY THE PRESSURE. THERE IS ALSO A VALVE FOR RAPIDLY VENTING PRESSURE IN THE CHAMBER INTERMITTENTLY AND A DELIVERY CONDUIT FROM ITS CHAMBER FOR THE FLUIDIZED POWDER.

Sept. 20,1971 M. STAND ETAL 3,606,481

l POWDER FEEDING ASSEMBLY Filed oct. '22, 1969 z sheets-sheet 1 FIG.

7| 72 I, 7| 7o FIG. 5

B'J@ 64 m2 6. 2 Se 3 T- u z. 79| L 62 f i L wie-i 6T 69 82 INVENTORS.MILLE STAN D ALBERT H. STREICHER JOHN P. CHANDLER THEIR ATTORNEY.

Sept. zo, 1911 M. STAND mL 3,606,481

POWDER EEEDING ASSEMBLY Filed Oct. 22. 1969 2 Sheets-Sheet 2 2.4.INVENTORS.

5| MILLE sTAN 48 ALBERT H. sT CHER JOHN P. CHANDLER THEIR ATTORNEY.

United States Patent Oihce 3,606,481 POWDER FEEDING ASSEMBLY MilleStand, New York, and Albert H. Streicher, Bronx, N .Y., assgnors toSealectro Corporation, Mamaroneck,

c o Filed Oct. 22, 1969, Ser. No. 868,487

Int. Cl. B65g 53/40 U.S. Cl. 302-50 3 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a feeder for delivering metal or other powdersin a fluidized state to a powder spray device, such as a plasma gun, aame spray gun, or any other apparatus. Powdered materials, such asplastics, ceramics, metals, or mixtures thereof, may be sprayed directlyonto substratesl to form a continuous coating and the rate of feedvaries with the nature of the powder or powders being sprayed and thematerial forming the substrate and its surface characteristics.

The powder from a reservoir is entrained into the carrier gas and thecombined gas and powder are conducted through a conduit to a hot zone,such as a plasma or llame jet where the particles soften and melt. Theycontinue their movement and impinge on a substrate to form. a coating.

The principal object of the invention is to provide an apparatus whichfeeds the powder at a unifonm, predetermined rate which can be varied.

Another object of the invention is to provide an apparatus through whichthe powder freely flows in a liuikiized state with a substantiallyconstant concentration of the powder in the carrier gas so that itseventual application in a softened state as a coating to a substrate canbe of uniform thickness.

Methods of aerating granular particles in order to improve their flowproperties are known in the art. A carrier gas at a controlled velocityand pressure is introduced into the powder reservoir at a graduallyincreas.- ing rate. The bed expands until the particles begin to Imoveand these particles are supported on the gas stream. The top of thedense-phase bed has a well-defined level resembling a boiling liquid. Asthe gas velocity is increased, entrainment of the particles in thecarrier gas increases to a point where the bedv level disappears anld asingle dilute-phase suspension is present through the entire vessel.

Yet another object of the invention is to provide an improved powderfeed apparatus wherein the rate of feed of the powder can be varied bychanging the speed of a feed screw which delivers powder from areservoir to a uidizing chamber, by varying the speed of the motorrwhich pumps the gas and by varying the pressure of the gas feed intothe chamber.

In the drawings:

FIG. 1 is a front elevation of an apparatus of the presnt invention;

FIG. 2 is a side elevation thereof, this view being taken on line 2-2 ofFIG. 1;

3,606,481 Patented Sept. 20, 1971 FIG. 3 is a section taken on line 3-3of FIG. 2;

FIG. 4 is a vertical section taken through the housing sections;

FIG. 5 is a section taken on line 5 5 of FIG. 1.

The powder feed assembly of the present invention is mounted on .achassis 10 which supports a motor 12 with a speed reducer 14 to furnisha speed of about 48 r.p.m. in the motor output shaft 16. A pulley 18 isfast on this shaft and a belt 19 thereon drives two additional pulleys20 and 21 fast on shafts 22 and 24.

A housing is formed in two parts 26 and 28 in juxtaposition along aline29. A Ipowder lreservoir 30 is machined out of or otherwise formed inthe first section and is defined by spaced walls 31 and 32 havingaligned holes 34 serving as bearings for shaft 22 which has a singleradial spoke 36 carried by a hub 38 fast thereon and rwhich supports anarm 37 which agitates the powder on the bottom wall 39 of the powderreservoir.

The powder reservoir is further defined by two additional opposed walls40 and 41 and a feed opening 42 in the top wall is closed by a closurecap 44. An opening 45 in the lower wall permits the powder to descendonto a screw conveyor 46 in a sump 48, the conveyor being fast on shaft24. The forward end of the conveyor is positioned in a round opening 49only slightly larger than the diameter of the conveyor, and the powder,already in a somewhat fluidized state, is fed into a powder fluidizingchamber 50 which is formed in the second housing section 28. Thischamber is generally hemispherical in shape and is closed by 'wall 32 offirst housing section 26.

The carrier gas, such as air, acetylene, nitrogen, helium, or mixturesthereof, under a pressure of about 60 lbs. p.s.i. is fed to a tube 51positioned in a machinedout section 52 in the concavely curved wall ofchamber 50. This tube has a number of discharge openings 54 and it isconnected outside the chamber within fitting 56 connected with a conduitS8 leading to a source of the carrier gas in which the powder is to beentrained. Another conduit 59 leads to a fitting 60 in wall 40 of thepowder reservoir. In this fashion, the pressures in chamber 50 andreservoir 30 are equalized and thus permit free movement of the powderto the fluidizing charnber. A needle valve 61 associated with fitting 60permits the pressures in both chambers to be varied for vario/us typesof powders.

One significant improvement in the assembly of the present inventionresides in a pulsating pressure relief device wherein the pressures inthe powder feed chambers are vented about times per minute. As a resultof this action, the pressure in this uidizing chamber is reduced,thereby preventing excess build-up of pressure in that chamberfacilitating the flow of powder through the discharge orifice.

A valve housing 62 supports a cylindrical valve member 64 driven by ashaft 66, for rotation. The valve member has two intersecting radialholes 67 and 68 and when each one of the holes become aligned with aconduit 69 leading to the powder chamber and with a discharge orifice 70in a fitting 71 on the valve housing, the pressure in the chamber dropsfor a fraction of a second to atmospheric pressure. The shaft is rotatedby a separate motor 72. This rapid oscillation of pressures impart ahigh measure of fluidity to the powder.

The powder in its highly fluidized state is discharged through conduits74 leading to fittings 76 and since there are generally two linesleading to the plasma torch, there are two of such conduits.

In a device of this character, it is necessary to ground all internalmetallic parts to discharge static electricity and this avoids bridgingof the powder. The shafts 22 and 24 are grounded by spring urgedgrounding plates 78 and 79 which engage the ends of the shafts. Thespring plates are mounted on an angular plate 80 secured to the chassis.A control box 82 has a knob 84 for controlling motor speed and an oi-onswitch 86.

It will be understood that motor 12 can be used for driving shaft 66associated with valve 64 although the separate motor gives good resultssince the occasional need to vary the speed of this shaft may not bepresent with respect to motor shaft 16. In the event that too much ortoo little powder is being fed by the screw conveyor, this can be variedby substituting a different screw.

Also, any valve for controlling pressure may be used in place of theneedle valve 61.

So far as the rate of feed of the powder is concerned, it will beappreciated that the faster the screw conveyor is turned the greater thequantity of powder that will be fed and to get the best results withdifferent kinds of powders, conveyors with different flight formationsmay be used. In other words, different powders will agglomerate orbridge in different ways regardless of the particle size of the powder.

What we claim:

1. A powder feed assembly including a housing formed with a powderreservoir and a powder uidizing chamber, the reservoir being formed witha sump at its lower end and a screw type conveyor in the sump to deliverpowder to the uidizing chamber, a rst conduit for delivering a carriergas under pressure to particles in the chamber for aerating the powder,a second conduit means connecting the chamber with the reservoir toequalize the pressures therein, a third conduit connected to the top ofthe chamber for delivering the uidized powder, and a rotatable valveconnected to a power shaft for intermittently venting the pressure inthe chamber to aid in the uidizing process.

2. The assembly of claim 1, wherein a motor is provided for rotating theconveyor and for turning the power shaft which operates the rotatablevalve.

3. The assembly of claim 1, wherein said rst conduit is provided with aplurality of holes for delivering the compressed gas to a number ofpoints in the chamber.

References Cited UNITED STATES PATENTS 1,132,715 3/1915 Greenstreet302--56 1,379,174 5/1921 Eichelberger 302-50 1,718,507 6/1929 VVenZelSO2-2A RICHARD E. AEGERTER, Primary Examiner

